In Arizona, the shooting death of a rancher blew the lid off simmering anger over border security and helped solidify support for a tough new immigration law. A similar eruption threatens in Virginia following the death of a Catholic nun in a car accident involving a man in the country illegally and accused of drunken driving.

The Benedictine Sisters of Virginia tried to discourage using the death of Sister Denise Mosier as a "forum of the illegal immigration agenda" and pleaded for a focus on "Christ's command to forgive."

"The sisters' mission is peace and love," said Corey Stewart, chairman of Prince William County's Board of Supervisors. "My mission is law enforcement and the protection of public safety."

Prince William County, about 25 miles southwest of Washington, D.C., stepped up its immigration enforcement in 2007 amid explosive growth of its Hispanic and immigrant populations. Under Stewart's leadership, the county implemented a local policy requiring police to determine the immigration status of all people arrested on suspicion of violating state or local laws.